Category: linux

I think most of us watched the movie Inception in which there was dream within a dream. It was a bit of confusing at some point. There is a Linux version of it 🙂 terminal within terminal provided by the fantastic tool tmux (terminal multiplexer). I use this tool during some troubleshooting scenarios when I Read More »

Today I have stumbled across a system resource utilization tool htop which is way more visual than top and it is easier to use too. For example, following is from my single core amazon cloud centos server. You can easily see that sorting is by CPU and if you want to change it, just press Read More »

Path MTU discovery that is in place today is relying on ICMP based MTU discovery i.e you send an oversize packet which can’t be forwarded by an intermediate host in the path because the next hop link has a lower MTU size, then the source host is notified by this hop which can’t forward this Read More »

In Linux, in the past I was using iproute2 and multiple routing tables to do some more advance stuff but when I became aware of Namespace, things really changed for me. Namespaces in Linux seem to be similar to logical systems in Junos. It seems to be a bit more than a routing instance in Read More »

Have you ever thought how the IP addresses are chosen/selected in icmp time exceeded error messages when you run a traceroute command? Recently I was analyzing an issue and this really made a difference in troubleshooting. I have done the analysis on an SRX firewall and a Linux device and I have got different results. Read More »

Today I wanted to test kamailio SIP server but I didn’t have prior experience on this software and I experienced several problems. After following the installation manual I created the username rtoo. root@debian1:~# cat .kamctlrc SIP_DOMAIN=sip.rtoodtoo.net root@debian1:~# kamctl add rtoo test123 MySQL password for user 'kamailio@localhost': new user 'rtoo' added so far so good. Then Read More »

My SecureCRT terminal window wasn’t displaying ANSI colors which was really annoying me. To be honest I dislike procrastination and finally I have enabled ANSI colors:) In Ubuntu installing “vim” package is sufficient I suppose. In other distributions you may have to install supplementary packages. Here are the possible steps; 1) Set your terminal to Read More »

I keep forgetting the “subtle” differences between access,modify and change attributes of an inode. I will try to take some note here for you and me. My file test.txt has got the text “abc” in it which is 3 bytes + 1 new line = 4 bytes and I pasted inode information below via stat Read More »

If you are keeping huge number of small files in your disks, this may one day cause running out of available inodes because of which even though you might have sufficient disk space, file system cannot create new files. Lets see how it works in my 1GB disk partition. The parameter “-i” allows us to Read More »

Have you ever received such an error when you are logged in as root? This error surprised me as I asked myself: Hang on a second! I am the super user, I should be able to change the permission of this regular file. [root@tux /]# chmod 644 /test chmod: changing permissions of `/test': Operation not Read More »